In the construction of buildings and, more particularly, the construction of institutional and commercial buildings, it is common and sometimes necessary to include interior room and space walls with door openings and interior windows called “lights” or glazing. The openings for doors and glazing are usually first roughly framed in with wall studs. Door frames and glazing frame assemblies are then attached to the studs and the assemblies are finished with wallboard, doors, and glazing.
In many commercial building interiors, wooden interior doors and door frames are preferred over metal doors and frames because exposed wood surfaces enhance the aesthetics of the interior spaces. Wood framing and mullions (including light-to-light mullions and door-to-light mullions) are also commonly used for interior glass panels including relites, sidelites (a.k.a. sidelights), borrowed lights, transom lights, vision lights, and any other light-transmitting panel installed in a wall or door (collectively, “glazed openings”). To reduce costs, wood assemblies for doors and door frames are often constructed with a shaved wood veneer adhered to the exterior of a manufactured fiber core material, such as medium density fiberboard (“MDF”). High-quality wood assemblies use similar core materials, but with a solid wood facing or trim that is precision-cut, not shaved. Typically, solid wood facing is slightly thicker than veneer, making it more durable, stronger, and longer lasting than veneer assemblies. However, solid wood surfaces typically provide more fuel for a fire than veneer, which reduces fire resistance of the assembly.
Modern fire codes and architectural practices require doors and door frames to be constructed in accordance with designs that have undergone fire testing performed by accredited testing facilities in accordance with established standard test procedures. One widely recognized test procedure is a 45-minute positive-pressure test performed by Intertek Testing Services (ITS/Warnock Hersey) of Boxborough, Mass., USA for rating in accordance with the following standards: NFPA 252, CAN4-S104, UBC 7-2 1997,ISO 3008, BS476 Part 22. Positive-pressure testing requires doors, door frames, glazed openings, and their frames and mullions to be tested as an assembly. The interior side of the assembly (facing toward the door when opened) is subjected to a furnace flame with positive pressure applied to the burn zone at a predetermined height from the bottom of the door. The tests permit only a limited amount of smoke to escape around the door and glazed openings.
In an attempt to meet positive-pressure testing requirements, known prior-art designs have included intumescent materials in the doors and door frames. When exposed to heat generated in a fire, intumescent materials quickly foam and expand, then char and solidify to provide a strong, fire-resistant seal that also inhibits the penetration of smoke around doors. Intumescent materials typically activate at temperatures in excess of 400° F., but may activate at higher or lower temperatures depending on the type of intumescent material used.
One known door frame design calls for workers at the construction site to apply adhesive-backed strips of graphite intumescent material against a door jamb surface called the rabbet (where the frame is stepped to receive the door). Such designs are subject to failure due to improper installation, tampering, and damage to the exposed intumescent material. Moreover, the only frames of this type known to comply with 45-minute positive-pressure testing are hollow metal frames.
Another known use of intumescent material is a door sold by VT Industries of Holstein, Iowa, USA that includes an intumescent strip embedded between a core of the door and a wood veneer along an edge of the door. However, to comply with 45-minute positive pressure testing, the VT Industries doors must be installed in a door frame that has been tested as an assembly with the VT Industries door. The only frames known to comply with 45-minute positive-pressure testing when used with the VT Industries door are metal frames to which intumescent material has been applied against the rabbet surface, as described above. Thus a need exists for a door frame assembly that complies with 45-minute positive-pressure test standards, which is more aesthetically pleasing and which does not expose the intumescent material to tampering and damage.
The present inventors have also recognized a need for an improved fire resistant sidelight frame. Summit Door, Inc., St. Paul, Minn., USA sells frames for sidelight openings that have successfully undergone 45-minute positive-pressure tests. This sidelite frame design uses intumescent strips inlaid against its top (header), bottom (sill), and sides (jambs) and between the glass panel and wooden stops that are fastened to the frame on both sides of the glass panel. This design requires the glass to be installed in the frame using metal glazing clips before the wooden stops are installed. The metal glazing clips are apparently necessary to provide support for the glass panel in the event of a fire. The metal glazing clips provide structural support for the glass panel, but add to the material cost as well as the time and cost involved in installing it. Thus there remains a need for aesthetically pleasing wood frames and mullions for glazed openings that will pass a 45-minute positive-pressure test without the need for expensive metal glazing clips.